The investigator has recently demonstrated that FceRI expression can be both down-regulated and up-regulated on human basophils and appears to be regulated by the IgE antibody. The receptor through which this regulation occurs is unknown, although FceRI or FceRII are reasonable candidates. The first aim addresses the question of whether FceRI expression is regulated in a similar manner in patients with various clinical conditions and whether it is regulated also on mast cells and monocytes in a similar manner. The second aim addresses some issues related to the mechanism of FceRI expression, focusing on the determination of whether there are coordinated changes in the FceRI-beta and -gamma subunits as well as closely associated tyrosine kinases. The functional consequences of FceRI up-regulation will be studied and pharmacological agents that regulate FceRI expression will be explored. The third aim focuses on determining the receptor involved in IgE-mediated FceRI upregulation. Whether receptor upregulation is associated with increased FceRI mRNA accumulation and the how the promoters for the receptor genes are regulated will also be studied.